Electrical injection of spin polarized electrons is observed at ferromagnetsemiconductor interfaces by analyzing the electroluminescence signal of GaAs/ (In,Ga)As light emitting diodes (LED) with injection layers of the metals Fe or MnAs. The circular polarization degree of the emitted light reveals a spin polarization for recombining electrons of about 1.5% to 2%. Time-resolved data on spin relaxation times indicate that the actual spin injection efficiency from both Fe and MnAs into GaAs is about 5% to 6%. The underlying injection mechanism can be explained in terms of a tunneling process.